It is important that electronic components and printed circuit boards be tested after the components have been soldered to the printed circuit boards. Several different approaches have been developed for testing the components and printed circuit boards, including functional testing, in-circuit testing, and manufacturing defect analyzers.
Functional testing uses a procedure of applying predetermined input signals and monitoring the output of a printed circuit board to determine if all of the components are present and operating properly on the circuit board. While functional testing provides a way of determining whether the P.C. board is functioning properly, it provides little or no information regarding the functioning of individual components on the board. Complex programming techniques have been used to provide limited information as to the location of non-functioning components on the board by carefully selecting input data and analyzing the output results. Such systems are complex, often costly to implement, and normally provide only vague information as to the location of malfunctioning components.
Because of the limitations of functional testing, in-circuit testing techniques have been used to individually test the components on the printed circuit board to determine if these components are working properly. This process uses a "bed of nails" tester to access each individual component and test that component individually. In this manner, non-functioning components can be identified and replaced to prevent the entire circuit board from being scrapped. This process works well for simple components where the circuit inside the component is known and can be easily tested. If the component being tested is very complex, or if the circuit inside the component is unknown, in-circuit testing may not achieve satisfactory results.
One very important potential problem that must be tested on every printed circuit board is whether all the pins of every component are in fact soldered to the circuit board. Functional testing may miss a particular pin, if the Xfunctions performed by that particular pin are not thoroughly tested in functional test. Testing for this type of fault is particularly difficult when the circuit inside the component is unknown, such as the case with application specific integrated circuits (ASICs). Because of the large number of ASICs and the complexity of these devices, it is often not feasible to design a functional test to isolate this particular component.
Manufacturing defect analyzers are another class of testing devices that provide simpler tests and are less expensive to implement. These devices are designed to locate manufacturing faults, such as shorts on a printed circuit board, missing integrated circuits, bent component leads, etc. Although these devices do a reasonably good job of finding shorts and gross analog faults, they are marginal when testing digital sections of the board as it is difficult to detect opens with this type of test when digital components are connected in parallel.
There is need in the art for a device and method which will determine whether all pins of a component including digital components are soldered to a circuit board in a simple and inexpensive manner. There is further need in the art for such a device and method which does not rely on knowledge of the operation of the circuit contained in the component. Although related U.S. Pat. No. 5,124,660 entitled Identification of Pin-Open Faults by Capacitive Coupling Through The Integrated Circuit by Ugur Cilingiroglu, issued Jun. 23, 1992 and related application Ser. No. 07/892,868 entitled Identification of Pin-Open Faults by Capacitive Coupling Through the Integrated Circuit Package by Ugur Cilingiroglu, Kevin Keirn and David Crook show the general concept of capacitive testing, it is important to increase the signal to noise ratio and to decrease the stray capacitance. The present invention meets these and other needs. Related U.S. Pat. No. 5,124,660 and related application Ser. No. 07/892,868, assigned to the assignee of this invention are specifically incorporated herein by reference for all that they teach.